As a method of removing particles adhering to a wafer to be processed, there has been conventionally known a liquid processing method in which, a solution containing mixture of ammonia and hydrogen peroxide is discharged onto the wafer while the wafer is being rotated, and then hydrofluoric acid is discharged onto the wafer while the wafer is being rotated so as to clean the wafer (see, for example JP 2002-329696A).
In this liquid processing method, the inventors have found that the use of an organic solvent for drying the wafer may generate marks such as watermarks on the wafer. Namely, after the wafer is processed by a process liquid containing an ammonia component (alkaline component) and by hydrofluoric acid, and then the wafer is dried by using an organic solvent, there is a possibility that the wafer has some marks.
Although the mechanism for the generation of marks on a wafer has not been clearly known yet, it is supposed that, when the surface of the wafer, which have been activated by the hydrofluoric acid, is exposed to the organic solvent with the ammonia component (alkaline component) being present in an outside atmosphere, the surface of the wafer is attacked by the ammonia component and the organic solvent.
The result of an experiment conducted by the inventors of the present invention shows that, even when a process liquid formed of an ammonia component (alkaline component) is not used as a process liquid, the presence of only a small amount of an ammonia component in the outside atmosphere may cause marks on the surface of a wafer W.